Conventionally, recording apparatuses having recording unit that records on a recording medium includes a recording medium conveying device. Also, the recording medium conveying device includes a conveying roller that conveys the recording medium toward the recording unit and a feeding roller that feeds the recording medium to the conveying roller. As for such a kind of a recording medium conveying device, for example, JP-H07-295311 (paragraph [0014], FIG. 1, etc.) discloses a conveying device including a pair of conveying rollers that conveys an image supporting body toward a photosensitive drum and a pickup roller that feeds the image supporting body to the pair of conveying rollers. JP-H7-295311 also discloses a technique for conveying rollers with a high degree of accuracy. In the technique, the thickness of the image supporting body is estimated by detecting the peak value of a current to drive the pair of conveying rollers in accordance with the estimated thickness of the image supporting body.
However, since the technique described in the JP-H7-295311 the thickness of the image supporting body is estimated by detecting the peak value of a driving current to be output for the pair of conveying rollers, the peak value of the driving current can be detected only after conveying is started by the pair of conveying rollers. Therefore, the pair of conveying rollers can not be controlled appropriately until the peak value of the driving current is detected and reflected to the pair of conveying rollers. This results in a problem that the image supporting body still can not be conveyed with a high degree of accuracy.
In addition to the conveying device described in JP-H7-295311, there has been known, for example, a recording medium conveying device including a conveying guide that conveys a recording medium in a U shape disposed between a conveying roller and a feeding roller. In the recording medium conveying device including the conveying guide, a flattened recording medium is deformed into a U shape to be conveyed, which causes a back tension due to the deformation of the recording medium.
Here will be described the back tension with reference to FIGS. 7A and 7B. FIGS. 7A and 7B are schematic views showing the internal mechanism of a recording medium conveying device 100 including a conveying guide 102, where FIG. 7A shows a state where a recording medium P is conveyed and FIG. 7B shows a state where the conveying of the recording medium P is stopped.
In the recording medium conveying device 100, the recording medium P is supplied and conveyed by a supply roller 101 while being bent into a U shape along the conveying guide 102. When the recording medium P is conveyed by the supply roller 101, the conveying roller 103 rotates in the same direction as the supply roller 101. Then, when a registering sensor 104 detects the recording medium P, the conveying roller 103 starts a reverse rotation (indicated by the arrow in FIG. 7A) to convey the recording medium P toward a target position.
During the conveying roller 103 conveys the recording medium P, the recording medium P is bent as shown in FIG. 7A. Therefore, a repulsive force acts on the recording medium P is borne on the conveying direction H, through which the recording medium P is conveyed by the conveying roller 103, as a back tension T. This deteriorates a conveying accuracy. In addition, when conveying roller 103 stops the conveying of the recording medium P as shown in FIG. 7B, the force in the conveying direction H by the conveying roller 103 becomes zero. Therefore, the effect of the back tension T becomes larger. This acts to the recording medium P to be returned from a desired stop position and also deteriorates a conveying accuracy when the recording medium is conveyed again.
The technique described in JP-H7-295311 the pair of conveying rollers is controlled in accordance with the thickness of the image supporting body. However, in such a kind of a recording medium conveying device in which a recording medium is deformed into a U shape to be conveyed, the deterioration of the conveying accuracy in accordance with the thickness of the recording medium is not necessarily appropriate to consider. The deterioration of the conveying accuracy due to the back tension T is more of a problem.